The invention relates to methods for producing improved tantalum conductive and resistive materials for use in ink jet heater chips.
Tantalum thin films are used in a variety of applications associated particularly with electronic equipment. For example, tantalum (Ta) may be used as a diffusion barrier between copper and silicon, a gate electrode in MOSFET""s, as an x-ray absorber in x-ray masks and as a protective overcoat above the resistors in thermal printheads for ink jet printing devices. Tantalum is typically sputter deposited as a mixture of two phases, namely alpha phase tantalum and beta phase tantalum. Beta phase tantalum has a tetragonal structure and is relatively harder and exhibits a much higher resistivity than the alpha phase which has a body-centered cubic structure and relatively lower resistivity.
A printhead for a thermal ink jet printing device usually contains a silicon substrate having conductive and resistive layers deposited thereon to provide electrical features which are used to heat and eject ink from the printheads. The ink jet ink may be corrosive to the various conductive and resistive layers deposited on the surface of the silicon. Accordingly, protective layers such as silicon dioxide and additional passivation layers of silicon carbide and/or silicon nitride are typically used in conjunction with the resistive and conductive layers. Deposition of each of the conductive, resistive and protective layers is generally conducted sequentially using a variety of deposition techniques. Each layer typically requires its own unique set of conditions for optimal deposition of the desired material. Once the layer is deposited, it may be subjected to patterning and/or etching steps to further define the characteristics of the layers and to provide a desired interconnection between certain layers. Each of the deposition, patterning and etching steps is time consuming and thus effects product throughput.
There is an ongoing need for improved manufacturing techniques for production of electronic components for thermal ink jet printheads.
With regard to the foregoing and other objects and advantages, the invention provides a method for producing a thin film tantalum layer of a desired phase for use in an ink jet printhead. The method comprises selecting a semiconductor substrate suitable for deposition of resistive, conductive, and protective layers thereon. The substrate is preferably etched prior to the deposition of the tantalum layer of the desired phase for a predetermined period of time. The substrate is then preferably heated at a selected temperature for a predetermined amount of time. The substrate may then be further heated or cooled to reach a desired substrate temperature suitable for sputtering the thin film tantalum layer of the desired phase. The substrate is maintained at the predetermined substrate temperature during the deposition of the tantalum film while the sputtering power is maintained at a predetermined input power level for a predetermined period of sputter time. The predetermined temperatures, times, and powers (collectively the factors) are selected in accordance with a mathematical relationship between the factors in order to produce the desired phase of tantalum in the tantalum thin film layer. The mathematical relationship between the factors is a regression equation that predicts the tantalum layer thickness, the tantalum layer sheet resistance, and the percentage of beta phase in the tantalum layer.
In another aspect, the invention provides a heater chip for use in an ink jet printhead comprising a semiconductor substrate wherein resistive, conductive, and protective layers are deposited thereon. The resistive, conductive, and protective layers may comprise thin film tantalum layers of a desired phase.
An advantage of the invention is that it provides a method for consistently producing thin film tantalum layers of a desired phase such that the tantalum thin films can be used for alternative applications such as conductors, resistors and cavitation resistant layers. Another advantage of the invention is that it provides a method for reducing production steps when manufacturing heater chips for use in an ink jet printer since pure phase tantalum films can be used instead of tantalum alloys. Another advantage of the invention is that it provides a method for reducing costs when manufacturing heater chips for use in an ink jet printer.
A further advantage of the invention is that it provides a method for producing thin film alpha phase tantalum conductors which can provide increased resistance to ink corrosion thereby extending the life of an ink jet printhead. Another advantage of the invention is that it provides a method for producing thin film tantalum overcoat layers of a desired phase which is suitable for enhancing cavitation resistance for a particular ink thereby increasing the life of an ink jet heater chip.